The invention relates, in general, to a gripper having four gripper jaws which can be moved in radially outward direction, for grabbing loads, in particular from above.
Grippers with four gripper jaws are known in general, particularly for loads which need to be gripped at the top and which have a cylindrical carrier opening. For this, the gripper jaws are introduced into the carrier opening and they are moved in radially outward direction, so as to secure the load by clamping action. A gripper of this type has a single-piece frame in which the gripper jaws are guided so as to be radially movable and axially fixed. The frame has four parallel longitudinal carriers spaced from one another at uniform radial distance as well as uniform angular distance and having upper and lower ends which are respectively fixedly connected to one another by a plate-shaped face element. The frame prevents shifting of the gripper jaws in the longitudinal direction of the frame, that is, they are guided in such a manner that only a radial movement is permitted. The gripper jaws are in contact with the arbor by means of the force exerted by the reset springs and actuated by the arbor via the piston-cylinder unit. The longitudinal carriers and the face elements form four shafts which extend radially outward, for receiving the gripper jaws, with an arbor disposed centrally between the longitudinal carriers in parallel relationship. The arbor can be guided through an opening in the upper plate element to the exterior, and, at least over a portion of its lengths tapers downwards. The arbor can be shifted in longitudinal direction by means of a piston-cylinder unit which is securely fixed to the upper plate element, whereby the gripper jaws are respectively in contact with the arbor as a consequence of a force applied by a reset spring. The contact surfaces of the gripper jaws are configured in at least the region of contact in conformity to the outer surface area of the arbor, such that a longitudinal shifting movement of the arbor is respectively converted into a radially directed movement of the gripper jaws. In this manner, it is assured that the movement of the arbor in the longitudinal direction is converted into a radial movement of the gripper jaws.
A disadvantage of known grippers is that the assembly thereof includes a frame and gripper jaws, which are complicated to make and thus incur considerable expenditures.
It would therefore be desirable and advantageous to provide an improved gripper which obviates prior art shortcomings and which can be economically produced with reduced manufacturing and assembly expenditures and obviating the afore-stated drawbacks.
According to one aspect of the present invention, a gripper is provided having gripper jaws, wherein each gripper jaw is formed by a plate-shaped central element and at least two lateral elements which extend parallel with respect to one another and which are disposed laterally with respect to the central element, which lateral elements respectively are provided with a depression which is directed to the outer side of the gripper jaw. The depression may have a cross section in the form of an isosceles triangle, with a base side extending parallel to the longitudinal carriers and two shorter roof sides directed inwardly toward the arbor and having same length, whereby the two ends of the base side are provided with pockets for receiving the ends of a leaf spring, with the leaf spring, having an the outer side for central abutment of a tensioning element provided at the associated longitudinal carrier and engaging in the depression. Alternatively, the cross-section of the depression may have a projection which is directed away from the arbor into the depression and which is opposed by a longitudinal side extending parallel to the longitudinal carriers, with the leaf spring in the relaxed condition extending parallel to this longitudinal side. Secured to each of the ends of the leaf spring is a tensioning element which engages in the depression and is arranged at the associated longitudinal carrier, whereby the tensioning element and the projection are configured to respectively effect a corresponding reset force to move the gripper jaw in outward direction. The face elements are made from sheet metal, and the longitudinal carriers are made either of longitudinal profiles or from the legs of at least four U-shaped metal sheets, whereby the metal sheets are arranged in such a way that they provide a central free space of quadratic cross-section and are disposed, respectively by an angle of 90 degrees, in an offset manner about the central axis of the arbor. This sheet metal configuration can be made in a highly cost-efficient manner and can selectively be provided with equally highly economic longitudinal profiles, for example, angle profiles. The latter also is more appealing in appearance.
Exchange of the grippers can be easily implemented, when the piston-cylinder unit is connectable to the upper face element by means of a connector in the form of a bayonet coupling. Suitably, the arbor may include an upper and a lower arbor element which can be releasably connected to one another, whereby the upper arbor element is disposed in the piston-cylinder unit and the lower one is disposed in the frame. In a simple manner, the connector may includes pin-shaped closing elements which are arranged at the piston-cylinder unit and extend in the longitudinal direction of the cylinder beyond the outer contour, and which have thickened ends for passage through complementary openings of the face element which openings are tapered in circumferential direction. The closing elements are introduced into the tapered portion by turning the entire piston-cylinder unit.
To prevent an inadvertent release of this connection between the piston-cylinder unit and the frame, for locking at the piston-cylinder unit, there is provided a locking element which latches in a depression or through-opening in the face element.
In order to move the gripper jaws in outward direction only when the gripper is fully positioned on the load, it may be suitable to provide an annular control element which emits a control signal when the gripper has been fully positioned on the load.
According to another feature of the present invention, the plate-shaped elements of the gripper jaws and the U-shaped metal sheets can be cut to size by laser from sheet metal. In this way, manufacture of the gripper is highly cost-efficient. Manufacture may be simplified and cost-efficiency enhanced, when the arbor is designed in a rotation symmetric manner and the carrier opening is cylindrical.